<!DOCTYPE html>
<html lang="zh">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>练习</title>
    <script>

        // debugger        //  在代码中打了一个断点
        console.log(a)      // 2

        var a=1
        console.log(a)      // 1

        function a(){
            alert(2)
        }
        var a=3 
        console.log(a)      //3

        var a=function(){
            alert(4)
        }

        console.log(4)      //4

        var a

        console.log(a)      //4

    </script>
</head>
<body>
    
</body>
</html>